1. Field of the Invention
The invention relates to semiconductor processing technology and, in particular, concerns a magnetoresistive random access memory (MRAM) device and method of fabricating the same.
2. Description of the Related Art
MRAM is a memory device that comprises a plurality of bits or elements that can be in at least two logic states in a non-volatile manner. Each bit comprises a magnetoresistive (MR) material whose electrical resistance varies with the magnetization of the MR material. Thus, selective magnetization of the bit's MR material permits the bit to be programmed into different resistive states.
To alter the state of the MRAM bit, a sufficiently strong magnetic field with a predetermined field pattern is applied to the bit, causing the net magnetization of the bit to be altered, and remain altered after the field is removed. Such magnetic field is typically generated by a current flowing through a conductor adjacent to the bit.
The conductors that provide the magnetic field for altering the state of the bits typically form a grid pattern, and the bits are typically located at the intersections of the grid. Thus, to alter the state of a bit that is located at a given intersection, selected currents are passed through the two intersecting conductors. The selected currents are selected such that magnetization of the bit changes only when subjected to a net magnetic field due to both of the selected currents.
The bits and the conductors in two dimensional grid permits efficient arrangement of the bits, as well as addressing the bits. The spacing between adjacent bits partially determines the memory density of the MRAM. One of the factors that limit how close bits can be positioned is determined by magnetic field patterns generated by the conductors. As is known in the art, a magnetic field generally loops around the cross section of the conductor, and the field strength decreases as distance from the axis of the conductor increases. The MRAM bit is positioned from the conductor (more precisely, from intersecting conductors) such that the net magnetic field due to selected currents is able to magnetize the bit in a desired manner.
Any magnetic field beyond the intended use range is loosely referred to as a fringe field, and can extend beyond the intended bit significantly. Even though the field strength decreases with distance, the fringe field may be sufficiently strong enough to at least partially affect the magnetization of an adjacent bit. Thus the MRAM is limited in its density when using traditional implementation of the magnetic field producing conductors.